JPH0442517A - Manufacture of anticorrosive permanent magnet comprizing rare earth element - Google Patents

Abstract

PURPOSE:To obtain synthetic resin coating having excellent corrosion resistance by sequentially conducting a pretreating step, an activating step, a smut removing step and a forming step of the surface of a sintered magnet together with a phosphate treating step and a chromic acid treating step, and executing a synthetic resin coating step. CONSTITUTION:A pretreating step, an activating step and a smut removing step are conducted as surface treating on a rare earth element-iron-boron sintered permanent magnet, and a phosphate treating step and a chromic acid treating step are then conducted. The phosphate treating may be executed by dipping in solution containing titanium phosphate. The chromic acid treating may be generally performed by dipping in hot aqueous chromate anhydride.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing a highly corrosion-resistant rare earth permanent magnet, and in particular to a rare earth-iron permanent magnet in which the surface of a sintered magnet body is uniformly coated with a corrosion-resistant synthetic resin coating. The present invention relates to a method for manufacturing a boron-based sintered permanent magnet.

(Prior Art) Rare earth permanent magnets are widely used in the fields of electrical and electronic equipment due to their excellent magnetic properties and economic efficiency, and in recent years there has been an increasing desire for higher performance. Among these, Nd-based rare earth permanent magnets in particular have lower raw material costs than Sm-based rare earth permanent magnets because they have more abundant Nd, the main element, than Sm, and do not require the use of large amounts of CO.
It is a permanent magnet material with extremely superior magnetic properties that far exceeds that of Sm-based rare earth permanent magnets, so not only can it replace small magnetic circuits that have conventionally used Sm-based rare-earth magnets, but also hard ferrite can be used from a cost perspective. It is also being widely applied to fields where electromagnets were used. However, rare earth metal materials such as Nd generally have the drawback of being easily oxidized in a very short time in humid air. This oxidation causes not only surface oxidation in which oxides are produced on the magnet surface, but also so-called intergranular corrosion, in which corrosion progresses from the surface to the inside along grain boundaries. This phenomenon is particularly noticeable in Nd magnets because of the presence of a highly active Nd-rich phase at the grain boundaries of Nd magnets. Corrosion at grain boundaries causes extremely large deterioration of magnetic properties, and if corrosion progresses during use,
Problems arise, such as degrading the performance of devices incorporating magnets and contaminating the area around the devices.

(Problem to be Solved by the Invention) Various surface treatment methods have been proposed to overcome the drawbacks of rare earth permanent magnets, especially Nd-based magnets, but none of these methods is perfect as a corrosion-resistant surface treatment. do not have. For example, with synthetic resin coatings made by spray painting, powder coating, or electrodeposition coating, rust occurs under the film due to the hygroscopicity of the resin, and with vapor phase plating methods such as vacuum evaporation ion sputtering and ion blating, It costs too much
Additionally, there were disadvantages such as the inability to coat circular holes and grooves.

Among these surface treatment methods, in the case of synthetic resin coating, the dirt and oxide film on the surface of the magnet were conventionally removed by degreasing, shot blasting, etc. as pretreatment; Since it is not possible to obtain sufficient corrosion resistance with pre-treatment, we fundamentally reconsidered the base treatment, which has a greater influence than the corrosion resistance of the synthetic resin coating itself, and decided to provide a synthetic resin coating with excellent corrosion resistance. be.

(Means for Solving the Problems) In order to solve the problems, the present inventors investigated various methods of surface treatment for synthetic resin coating, and found that phosphate treatment and chromic acid treatment, which are used in iron products, The present invention was completed based on the discovery that the performance of synthetic resin coatings can be maximized by temporarily inhibiting rust using a combination of treatments.

The gist of the present invention is to provide a method for producing a rare earth-iron-poron-based sintered permanent magnet, in which the surface of the sintered magnet body is subjected to a pretreatment step, an activation treatment step,
A method for manufacturing a corrosion-resistant rare earth magnet, characterized in that a phosphate treatment step and a chromic acid treatment step are sequentially performed in combination as a smut removal step and a chemical conversion treatment step, and finally a synthetic resin coating step is performed.

The present invention will be explained in detail below.

First, the composition of the rare earth-iron-boron based sintered permanent magnet (hereinafter referred to as rare earth magnet) to which the method of the present invention is applied is that the rare earth metals are Sc, Y, La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb,
At least one of Dy, Ho, Er, Tm, Yb, and Lu, the content of which is 5 to 40% by weight
It is. Further, 50 to 90% by weight of Fe and C.

up to 15% by weight, B from 0.2 to 8% by weight, and additives such as Ni, Nb, Al, Ti, Zr, Cr, and V.
, Mn, Mo, Si, Sn+ Ga * Cu + and Zn in an amount of 8% by weight or less, and in addition to this, C, O.

It contains industrially unavoidable trace impurities such as P and S.

As mentioned above, rare earth magnets with such a composition are
Since it lacks corrosion resistance as it is, surface treatment with excellent corrosion resistance is required.Hereinafter, the surface treatment method employed in the present invention will be explained in the order of steps (1) to (6).

(1) Pretreatment step...4 types i) to iv).

i) Rust Removal Rust removal is performed for the purpose of removing the oxide film on the surface of the rare earth magnet, and is accomplished by polishing with a grindstone or puff, barrel polishing, sandblasting or honing, brushing, etc.

This removes rust, dirt, and other impurities from the surface of the rare earth magnet.

it) Solvent Degreasing Solvent film - The purpose of the solvent film is to remove oil and fat stains from the surface of rare earth magnets. It is done by spraying. This removes organic stains such as press oil, cutting oil, and antirust oil.

1ii) Alkaline Degreasing Alkaline degreasing, like the above-mentioned solvent degreasing, is performed for the purpose of removing oil and fat stains from the surface of rare earth magnets. Generally, solvent degreasing is preliminary degreasing, and alkaline degreasing is corresponds to the main degreasing cleaning. The components of the alkaline degreasing solution are sodium hydroxide, sodium carbonate, sodium orthosilicate, sodium metasilicate, trisodium phosphate, sodium cyanide, chelating agents, etc. The rare earth magnet may be immersed in the mixture heated to room temperature to 90 DEG C. Also, cathodic electrolysis, anodic electrolysis, or PR electrolysis may be performed at the same time as this alkaline degreasing.

iV) Pickling Pickling is generally carried out for the purpose of removing the oxide film that could not be removed in steps i) to 1ii), or the alkaline film using an alkaline degreasing solution or the oxide film generated during electrolytic cleaning. The pickling solution contains at least one of sulfuric acid, hydrofluoric acid, nitric acid, hydrochloric acid, permanganate oxalic acid, acetic acid, formic acid, hydroxyacetic acid, and phosphoric acid in a total of 1 to 40%.
It is an aqueous solution containing 18 to 40% by weight, preferably 18 to 40% by weight. The rare earth magnet is immersed at a temperature of 10 to 60° C. and pickled. This removes oxides, hydroxides, sulfides, metal salts, and other impurities on the surface of the rare earth magnet.

The above four types of pretreatment steps i), ii), 1ii), i
v) depends on the quality and degree of contamination on the surface of the rare earth magnet. After treatment, it is necessary to thoroughly rinse with water.

(2) Activation treatment process In the activation treatment process, the surface energy state of the rare earth magnet surface is increased in advance, and the subsequent phosphate treatment, chromic acid treatment, and synthetic resin coating film and magnet surface are This is done to improve the adhesion between the two. This treatment allows the surface of the rare earth magnet to adhere firmly to the synthetic resin coating, thereby preventing corrosive substances from entering the surface of the rare earth magnet, thereby improving corrosion resistance. The chemical solution (activation treatment solution) used for activation has almost the same components as the above-mentioned pickling solution, but may have a lower concentration than the pickling solution. That is, an aqueous solution containing a total of 1 to 20% by volume, preferably 1 to 15% by volume of at least one of hydrochloric acid, sulfuric acid, hydrofluoric acid, nitric acid, permanganic acid, oxalic acid, acetic acid, hydroxyacetic acid, and phosphoric acid. be. If you want to further enhance the activation effect, it is recommended to add a small amount of surfactant. Examples of surfactants include soaps such as sodium laurate, sodium myristate, sodium palmitate, and sodium stearate, or branched chain alkylbenzene sulfates, linear alkylbenzene sulfates, alkanesulfonates, a- A total of 3% by weight of at least one of synthetic anionic surfactants such as olefin sulfate salts, cationic surfactants such as alkyldimethylbenzylammonium chloride, and nonionic surfactants such as nonylphenol polyoxyethylene ether. It is desirable to add it above.

Furthermore, in order to extend the life of the activation treatment solution, a metal ion sequestering agent may be added. Namely, among inorganic metal ion sequestrants such as sodium birophosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, and sodium hexametaphosphate, and organic metal ion sequestrants such as citric acid, gluconic acid, tartaric acid, diethylenetriaminopentaacetic acid, and hydroxyethylenediaminetetraacetic acid. At least one or more types may be added in a total amount of 5% by weight or less. Activation is carried out by immersing a rare earth magnet in an aqueous solution containing appropriate amounts of the above acids, surfactants, and sequestering agents at a temperature of 10 to 80'C.

(3) Smut removal process Smut removal is performed after rinsing with water after the activation treatment process. After this smut removal, phosphate treatment, chromic acid treatment, and synthetic resin coating are performed to remove the synthetic resin coating. The effect of further improving the adhesion with the magnet surface can be obtained.

This smut removal is a process in which trace amounts of impurities that remain on the magnet surface are removed by physical adsorption or magnetic attraction.Specific methods include removal by brushing, water or air spray. Removal by ultrasonic waves, etc. can be mentioned.

(4) Phosphate treatment step When coating steel materials with synthetic resins, it is widely and generally practiced to form various chemical coatings on the surface of the material as a base treatment. Phosphate treatment can also be applied to patented earth magnets featuring iron as a type of chemical conversion treatment for the base of synthetic resin coatings.

The phosphate film itself formed on the surface of the magnet acts as a rust preventive agent, and at the same time, its anchoring effect further improves the adhesion to the synthetic resin coating.

Note that phosphates are classified into zinc-based, zinc-calcium-based, manganese-based, and iron-based based on the film structure formed, and all of them are effective for the magnet.

Among the phosphate treatments, zinc phosphate is crystalline, and if the fine crystals adhere uniformly and densely to the entire surface of the magnet, corrosion resistance and adhesion are higher (such a film can be obtained). A surface conditioning process may be added as a process before the zinc phosphate treatment.The principle of surface conditioning is that titanium phosphate generally forms a large number of phosphates on the metal surface as a sparingly soluble colloid. It is thought that the chemical adsorption occurs by creating a crystal nucleus for titanium phosphate.Specifically, if it is placed in a solution containing titanium phosphate at room temperature to 45℃ for about 0.5 to 1 minute, good.

(5) Chromic acid treatment step By performing so-called chromate treatment, which involves immersion in a hot aqueous solution containing anhydrous chromic acid (CrO2), after phosphate treatment, the corrosion resistance is further improved than by phosphate treatment alone.

This chromic acid treatment consists of 1 to 100 g of chromic anhydride/I2
Generally, it is immersed in a hot aqueous solution containing 20 to 80°C for 5 seconds to 5 minutes.

In addition, the draining and drying conditions after treatment are also a governing factor for corrosion resistance, and it is necessary to thoroughly wash with water and dry thoroughly until chromic acid is no longer detected in the washing water.

By carrying out the above five steps (1) to (5) in sequence, the base treatment for the synthetic resin coating described below is sufficiently performed, and the surface of the sintered magnet body and the synthetic resin coating are strongly adhered to each other, resulting in high Provides corrosion resistance.

(6) Synthetic resin painting step The final step of the surface treatment is a synthetic resin painting step. After treatment with chromic acid, thoroughly wash with water and dry before entering the main process. As for the synthetic resin, it is necessary to select one that has high hardness as a coating film (and has excellent adhesion, heat resistance, weather resistance, etc.), and epoxy synthetic resin is preferable.This epoxy synthetic resin is mainly used in an organic solvent solution. It is finished by spray painting or electrodeposition, or by powder coating as a fine powder.The thickness of the coating film depends on the performance of the synthetic resin, but is 5 to 100 μm, preferably 10 to 50 μm, and is free from pinholes, scratches, etc. It must be painted under appropriate conditions to avoid any unevenness.

A rare earth-iron-boron-based sintered permanent magnet with excellent corrosion resistance and durability can be obtained by performing a series of base treatment and surface treatment in steps (1) to (6) above.

Hereinafter, embodiments of the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Example 1) 32.0% by weight of Nd was dissolved by high frequency melting in an Ar atmosphere.
, Tb 2.0% by weight, B 1.1% by weight, F
58.4% by weight of e, 5.0% by weight of Go, 1.
Ingots containing 0% by weight and 0.5% by weight of Ga were produced. This ingot was coarsely crushed with a show crusher and further finely crushed with a jet mill using N2 gas to obtain a fine powder with an average particle size of 3.5 μm. Next, this fine powder was filled into a mold to which a magnetic field of 10,0000e was applied, and 1. Molding was carried out at a pressure of Ot/crrf. Next, it was sintered in vacuum at 1,090°C for 2 hours, and then aged at 550°C for 1 hour to obtain a permanent magnet. A rectangular test piece measuring 30+nn+×30mm×3mmt was cut out from the obtained permanent magnet. The easy axis of the magnet was made to coincide with the thickness direction.

This rare earth magnet test piece was subjected to the following surface treatment.

(1) Pretreatment process Steel-thin rainbow blast...1 minute.

(2) Activation treatment process Immerse for 1 minute in the activation treatment solution described below.

Acetic acid... Hydrochloric acid 2% (v/v) 2% (v/v) Sulfuric acid... 2% (V/V) Sodium laurate... 1 geI! .

(3) Smut removal process Underwater ultrasound...1 minute.

(4) Zinc phosphate treatment step The composition of the zinc phosphate bath used in the present invention is as follows (
All parts are made by Nippon Paint (part names).

■Pranozin 16N-18T: Zinc phosphate treatment agent (main ingredients: monovalent zinc phosphate and heavy metals (Mn)) 4% V/V, ■Brymer 40: Neutralizing agent (caustic alkali)...1.2
Adjust the concentration to %V/V, temperature 50-60℃, immersion time 5-10
Chemical conversion treatment was performed in minutes.

(5) Chromic acid treatment The bath composition and treatment conditions of the chromic acid bath are as follows.

Chromic anhydride concentration = 3 to 5 g/I2, temperature 50 ± 5°C,
The immersion time was 1 to 1.5 minutes, and the water washing was thoroughly washed by running pure water at 25°C for 3 minutes, and then dried at 60°C for 10 minutes.

(6) Synthetic resin coating Using cationic electrodeposition paint Nisbier 9VS (epoxy-based synthetic resin, trade name manufactured by Shinto Paint ■), using the test piece as the cathode and the 5US316 material plate as the anode, at a temperature of 28°C and a voltage of 1
Electrodeposition coating was performed under the conditions of 70V and 3 minutes. After washing with water and air drying, the resin layer was held at 180° C. for 30 minutes to adhere the resin layer. The thickness of the resulting coating film was 20 μm.

After the above surface treatment was completed, a corrosion resistance test was conducted under the following conditions, and the results are shown in Table 1.

[Corrosion Resistance Test] A moisture resistance test was conducted at 80° C. and 90% RH to determine the durability time until appearance abnormalities such as rusting and blistering occurred.

(Comparative Example 1.2) As Comparative Example 1.2, surface treatment was carried out under the same conditions as in Example 1, except that the surface treatment conditions were set as shown below and in Table 1, and the results of the corrosion resistance test are shown in Table 1. Described in.

Comparative Example 1 Dichromic acid treatment step...None Comparative Example 2: Zinc phosphate treatment step...None Dichromic acid treatment step...None These results demonstrate the effectiveness of the combination of phosphate treatment and chromic acid treatment of the present invention. It can be seen that the corrosion resistance and durability are significantly improved.

(Effects of the Invention) The present invention is characterized in that when coating the surface of a rare earth-iron-boron sintered permanent magnet body with a corrosion-resistant synthetic resin, a combination of phosphate treatment and chromic acid treatment is applied to the base as a chemical conversion treatment. This method provides excellent corrosion resistance that has never been seen before, and the deterioration of magnetic properties due to changes over time is extremely small, making it extremely effective as a highly reliable method for producing magnets.

Patent applicant: Shin-Etsu Chemical Co., Ltd. Agent Patent Attorney Ryo Yamamoto -Tomoe 1rC”-

Claims (1)

[Claims] 1. In a method for producing a rare earth-iron-boron sintered permanent magnet, the surface of the sintered magnet body is subjected to a phosphate treatment step and a chromic acid treatment step as a pretreatment step, an activation treatment step, a smut removal step, and a chemical conversion treatment step. sequentially used in combination with
A method for producing a corrosion-resistant rare earth permanent magnet, the method comprising finally carrying out a synthetic resin coating process.